Mycobacterium tuberculosis is an obligate aerobe and only survives in oxygenated areas.
Exact reason for TB’s propensity to reactivate in the upper lobes is not clear but two proposed rationales:
- Relatively higher oxygen tension compared to lower lobes (The lower lobes have better perfusion and therefore better V/Q match => greater gas exchange and more CO2 content compared to upper lobes)
- Impaired lymphatic drainage in upper lung lobes reduces the ability of the immune system to mount a response to the pathogen and clear it
- Allen EA. Tuberculosis and other mycobacterial infections of the lung. In: Thurlbeck WM, Churlbeck AM, eds. Pathology of the lung. 2nd ed. New York, NY: Thieme Medical, 1995; 229-265.
- Goodwin RA, DesPrez RM. Apical localization of pulmonary tuberculosis, chronic pulmonary histoplasmosis, and progressive massive fibrosis of the lung. Chest 1983; 83:801-80
- Dolin, [edited by] Gerald L. Mandell, John E. Bennett, Raphael (2010). Mandell, Douglas, and Bennett’s principles and practice of infectious diseases (7th ed.). Philadelphia, PA: Churchill Livingstone/Elsevier. pp. Chapter 250.